Various antipollution devices for use in automotive exhaust systems are known. Two common examples are the catalytic converter and the diesel particulate filter (“DPF”). Such known antipollution devices typically include housings in which certain components are positioned.
Within the main portion of the housing of a typical antipollution device is assembled a honeycomb-like structure (i.e., a “brick”) most commonly made of a suitable ceramic substrate or similar material. (Other materials, e.g., stainless steel honeycombs, are also sometimes used as the substrate.) The brick provides a structure to which is applied various precious metals which act as the catalyst. The brick is a very fragile structure and is easily damaged, and because of this it is usually wrapped in a supportive, intumescent, mat inside the main portion of the housing. As is well known in the art, the main portion of the housing typically is sized to accommodate the brick and the mat therein, and the sizing of the housing is very important.
In general, the mat is critical to the overall performance of the antipollution device. The mat is required to seal the surfaces between the outer perimeter of the brick and the inner perimeter of the housing (i.e., in the main portion) to ensure that substantially all exhaust passes through the brick and is exposed to the catalyst, so that the undesired emissions are processed. In addition, the mat also imparts the proper forces within the housing to ensure the brick is not fractured due to excessive force, but is subjected to sufficient force to properly maintain and hold the brick in the correct position within the housing without slippage. As is well known in the art, according to design, the mat is to be compressed to a predetermined extent (e.g., so as to have a predetermined gap bulk density (“GBD”)).
As is well known in the art, housings for antipollution devices are provided in a variety of shapes in cross-section. For example, in cross-section, the housings may have the following shapes: round, ovals, rectangles, squares, trapezoids, and many variations of such shapes, including irregular shapes. It is also known that antipollution device housings are often designed to receive a single brick, but alternatively are also often made with several bricks because of the performance requirements in a particular application.
A number of problems have arisen in connection with the known methods of manufacturing antipollution devices. The methods of the prior art have resulted in many failures due to inaccurate forming of the main portion and the transition portions in relation to the dimensions of the mat and the brick(s) which are assembled within the particular housing. For instance, if the housing is incorrectly formed too large, then the mat/brick subassembly slides in relation to the housing, resulting in damage to the brick and/or mat and, as a direct consequence, the immediate failure of the antipollution device when it is used. On the other hand, if the housing is sized too small or too tight, the antipollution device either cannot be assembled or the mat/brick subassembly is damaged during the assembly process, which typically results in impaired performance or failure of the antipollution device.
Various methods of assembling the brick and the mat in the housing are known in the art. For instance, it is known to provide a housing which is somewhat larger than required for a particular brick/mat subassembly. In this situation, the housing is formed from a workpiece which is reduced in size after the brick/mat assembly is positioned in the workpiece, to the required size and shape for the brick/mat subassembly. It is also known in the prior art to provide a housing which is required to be expanded in order to accommodate the brick/mat subassembly.
If the housing is properly formed to the correct dimensions of the individual brick/mat assembly, then the assembled antipollution device will satisfy the necessary GBD and/or other required inspection criteria. However, because the tolerance is relatively fine, even a small deviation from the required dimensions of the housing can result in an unacceptable assembly.
Depending on the variability of the brick and the mat, each housing may be required to be sized to unique and variable sizes based on the components that will be assembled within the housing. However, it is also known that, for a particular design, each shell may be reduced to substantially the same inner design dimensions, if the brick and the mat are manufactured to suitable tolerances.
In the prior art, where a shell has a non-round profile (e.g., oval) and the workpiece is required to be reduced by more than approximately 2 millimeters, the shell is not satisfactorily formed. This is because, in the prior art, the tool segments are moved toward a common center as the workpiece is formed into the shell (FIG. 1A). However, in the prior art, the tool segments (or jaw segments) are not movable at a uniform rate (i.e., the prior art jaw segments do not engage the workpiece substantially simultaneously), resulting in ridges (not shown) in the shell when the size reduction is greater than about 2 millimeters. Because many designs now require far more than a 2 millimeter reduction, this means that the shell or housing is often not satisfactorily formed.
In the prior art, the housing is often formed in a process in which at least two, and sometimes three or more different machine heads are used in an attempt to address this problem, i.e., in an attempt to ensure that each housing is appropriately formed. Using this many machines involves a relatively high unit expense and also requires time to be spent in the manufacturing process moving the workpiece between machines. Also, the use of multiple machines has not necessarily resulted in satisfactory reduction of the non-round profile by 2 millimeters or more.
A typical prior art tool assembly 20 to be used for reduction of a non-round profile by 2 millimeters or more is shown in FIGS. 1A-1D. (As will be described, the remainder of the drawings illustrate the present invention.) As is well known in the art, the tool assembly 20 typically includes a ring portion 17 with a round tapered inner bore therein defined by an inner surface 19 and an inner segmented subassembly 21 including a number of jaw segments 22. However, where the workpiece is reduced by 2 millimeters or more to form the non-round housing, the prior art tool assembly 20 has often provided unsatisfactory results, as described above.
As can be seen in FIGS. 1C and 1D, the jaw segments 22, when in an engaged condition (as shown in FIGS. 1A-1D), define a substantially oval design profile 24. As is well known in the art, internal surfaces 26 of the jaw segments 22 engage an outer surface of a workpiece (not shown in FIGS. 1A-1D) as the jaw segments move inwardly, each jaw segment 22 moving as indicated by the arrows “A” toward a common center “X” (FIG. 1C). The converging and forward movement of the jaw segments results from movement of a back plate (not shown) on which the jaw segments 22 are mounted toward the ring portion (FIGS. 1A, 1B) with the substantially round tapered bore therein. Also, the convergence during the forward movement of the jaw segments results from engagement of tapering side surfaces 28 (FIG. 1D) with the inner surface (not shown) defining the round hole in the ring portion, as the back plate is moved toward the ring portion.
As noted above, in practice, the prior art tool assembly generally does not provide a satisfactory housing with a non-round profile. The housing resulting from this processing typically has small ridges thereon. This defect appears to be due to each of the jaws having a slightly different geometry, but each also being urged inwardly by an inner surface of the ring portion which is round in cross-section, toward a common center.